In the Nordic countries Finland, Norway and Sweden, the most common regeneration method is planting after clearcutting and, often, mechanical site preparation (MSP). The main focus of this study is to review quantitative effects that have been reported for the five main MSP methods in terms of survival and growth of manually planted coniferous seedlings of Norway spruce ( (L.) Karst.), Scots pine ( L.) and lodgepole pine ( var. Engelm.) in clearcuts in these three countries. Meta analyses are used to compare the effects of MSP methods to control areas where there was no MSP and identify any relationships with temperature sum and number of years after planting. In addition, the area of disturbed soil surface and the emergence of naturally regenerated seedlings are evaluated. The MSP methods considered are patch scarification, disc trenching, mounding, soil inversion and ploughing. Studies performed at sites with predominately mineral soils (with an organic topsoil no thicker than 0.30 m), in boreal, nemo-boreal and nemoral vegetation zones in the three Fenno-Scandinavian countries are included in the review. Data from 26 experimental and five survey studies in total were compiled and evaluated. The results show that survival rates of planted conifers at sites where seedlings are not strongly affected by pine weevil ( L.) are generally 80–90% after MSP, and 15–20 percent units higher than after planting in non-prepared sites. The experimental data indicated that soil inversion and potentially ploughing (few studies) give marginally greater rates than the other methods in this respect. The effects of MSP on survival seem to be independent of the temperature sum. Below 800 degree days, however, the reported survival rates are more variable. MSP generally results in trees 10–25% taller 10–15 years after planting compared to no MSP. The strength of the growth effect appears to be inversely related to the temperature sum. The compiled data may assist in the design, evaluation and comparison of possible regeneration chains, i.e. analyses of the efficiency and cost-effectiveness of multiple combinations of reforestation measures.Picea abiesPinus sylvestrisPinus contortalatifoliaHylobius abietis

Interactions between soil water conditions and forest stands in boreal forests with implications for ditch network maintenanceSikström U., Hökkä H. (2016). Interactions between soil water conditions and forest stands in boreal forests with implications for ditch network maintenance. Silva Fennica vol. 50 no. 1 article id 1416. 29 p. Highlights• Ditch network maintenance (DNM) may influence soil water conditions less than initial ditching due to reduced hydraulic conductivity of the peat. • Stand stocking and management substantially influence soil-water conditions. • DNM can lower the GWL and increase tree growth.• DNM growth responses of 0.5-1.8 m 3 ha -1 yr -1 during 15-20-years in Scots pine peatland stands reported. • Greatest need for DNM in the early phase of a stand rotation.• Need for better understanding of the link between soil water and tree growth. AbstractAt sites with either peat or mineral soils in large areas of boreal forests, high soil-water contents hamper tree growth and drainage can significantly increase growth. Hence, areas covering about 15 × 10 6 ha of northern peatlands and wet mineral soils have been drained for forestry purposes. Usually ditches gradually deteriorate, thus reducing their functionality as drains, and ditch-network maintenance (DNM) might be needed to maintain stand growth rates enabled by the original ditching. This article reviews current knowledge on establishing the need for DNM in boreal forest stands, subsequent growth responses, and the financial outcome of the activity. The issues covered in the review are: (i) ditching, changes in ditches over time and the need for DNM; (ii) interactions between soil water and both stand properties and stand management; (iii) ground-water level (GWL) and tree growth responses to DNM; and (iv) financial viability of DNM. Conclusions about the current understanding of issues related to DNM are drawn and implications for DNM in practice are summarized. Finally, gaps in knowledge are identified and research needs are suggested.

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The objective of this study was to evaluate the potential of different water management options to mitigate sediment and nutrient exports from ditch network maintenance (DNM) areas in boreal peatland forests. Available literature was reviewed, past data reanalyzed, effects of drainage intensity modeled, and major research gaps identified. The results indicate that excess downstream loads may be difficult to prevent. Water protection structures constructed to capture eroded matter are either inefficient (sedimentation ponds) or difficult to apply (wetland buffers). It may be more efficient to decrease erosion, either by limiting peak water velocity (dam structures) or by adjusting ditch depth and spacing to enable satisfactory drainage without exposing the mineral soil below peat. Future research should be directed towards the effects of ditch breaks and adjusted ditch depth and spacing in managing water quality in DNM areas.

N-cycling was studied at three Norway spruce (Piceaabies (L.) Karst.) sites located within a distance of 30 km in southwest Sweden. Nitrate concentrations in soil water at 50-cm depth differed substantially between the three sites, annual site means being 0, 1, and 9 mg N•L−1. Using simulated runoff, the leaching of inorganic N from the two sites with the highest concentrations was estimated at, respectively, 7–8 and 19–30 kg•ha−1 during the hydrological year 1991–1992. The N-deposition measured as throughfall was 31 kg•ha−1 on the second site, suggesting that it was close to being N-saturated. The differences in nitrate concentration and estimated leaching across sites were not related to differences in forest growth or suggested symptoms of forest decline, such as canopy defoliation and nutrient deficiency. Nitrate concentrations were unrelated to N-deposition in an open field, but positively related to N-deposition in throughfall. However, the difference in N-leaching between the two main sites was much larger than the difference in N-deposition in throughfall. The difference in leaching seemed related to soil conditions. The soil with the highest leaching had the largest potential nitrification and a low C/N ratio (17–20) in the upper part of the profile. Nitrate concentrations in the soil water were positively related to the concentrations of arginine and 15N in foliage, which supports the use of these two variables as indicators of forests approaching N-saturation.

Wood ash additions of 3.3 and 6.6 t ha −1 reduced greenhouse gas (GHG) emissions from a spruce forest (Picea abies) on a minerotrophic drained organic soil. Emissions of carbon dioxide (CO 2 ), methane (CH 4 ) and nitrous oxide (N 2 O) were measured using static dark chambers for two years following the ash treatment. The CO 2 emission from the soil was significantly reduced by 17-23% by both doses during 2006-2008. The mechanism behind the reduction could not be related to a direct inhibition of soil C mineralization by the ash. The emission of N 2 O was also significantly reduced by 44 and 46% during the first year, mainly due to reductions in the winter emissions. Similar reductions of 34 and 50% were found in the second year for the low and the high wood ash, respectively. Increased pH of the soil due to the ash additions may have caused the effect. The control and amended soils consumed ambient CH 4 . The low wood ash dose increased the annual net CH 4 uptake rate by 9%, due to an increased winter uptake. No changes in tree growth could be detected over the short 2-year measurement period. The net effect of wood ash application was a reduction in the total GHG emissions during the first two years after the treatment.

Liming and (or) application of specific nutrients have been proposed as countermeasures to the acidification of forest soils in southern Sweden. The aim of this study was to investigate whether stem growth, crown transparency, and needle element concentrations of Picea abies (L.) Karst. growing on acidic mineral soils in southwestern Sweden are affected by additions of lime, lime plus P and K, or N in low doses (treatments: CaPK, Ca, N, CaPKN, and 2Ca2P2K). During the 5-year observation period following treatment with CaPKN there was a tendency to increased stem growth (possibly overestimated). The most plausible cause of this growth response was increased N availability in the soil, although the possibility that there was a minor effect of the PK application could not be excluded. None of the treatments affected the crown transparency. Several significant changes in elemental concentrations of current-year needles were associated with the treatments. The control plots in the experimental stands showed no severe damage or nutrient deficiencies despite the relatively acidic soils. These findings, together with the small treatment effects, suggest that there is no acute need for liming and (or) PK addition in P. abies stands on similar sites in southwestern Sweden.Résumé : Le chaulage et l'application de certains nutriments ont été proposés pour remédier à l'acidification des sols forestiers dans le Sud de la Suède. Le but de cette étude consistait à déterminer si la croissance de la tige, la transparence de la cime et la concentration des éléments dans les aiguilles de Picea abies (L.) Karst. croissant sur des sols minérals acides dans le Sud-Ouest de la Suède sont affectées par l'addition de chaux, de chaux avec P et K ou N à faibles doses (traitements : CaPK, Ca, N, CaPKN et 2Ca2P2K). Pendant la période d'observation de 5 ans qui a suivi le traitement avec CaPKN, la croissance de la tige a eu tendance à augmenter (cette augmentation est peut-être surestimée). L'explication la plus plausible de cette réaction est l'augmentation de la disponibilité de N dans le sol bien que la possibilité d'un léger effet dû à l'application de PK ne puisse être rejetée. Aucun des traitements n'a affecté la transparence de la cime. Plusieurs changements significatifs dans la concentration des éléments dans les aiguilles de l'année en cours sont associés aux traitements. Les parcelles témoins dans les peuplements qui faisaient partie du dispositif expérimental n'ont montré aucun dommage sévère ni déficiences en nutriments malgré des sols assez acides. Ces résultats, combinés aux effets négligeables des traitements, indiquent que le chaulage et l'ajout de PK ne sont pas absolument nécessaires dans les peuplements de P. abies sur des sites similaires dans le Sud-Ouest de la Suède.[Traduit par la Rédaction] Sikström 1727

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